Lattice Stiffening Research Articles

Pressure effects on the electronic structure, phonons, and superconductivity of noncentrosymmetric ThCoC2

The electronic structure, phonons, electron-phonon coupling, and superconductivity are theoretically studied in noncentrosymmetric superconductor ThCoC$_2$ as a function of pressure, in the pressure range 0 - 20 GPa. We found that the electronic band splitting induced by the spin-orbit coupling is enhanced under pressure. In spite of the overall stiffening of the crystal lattice, the electron-phonon coupling constant $\lambda$ increases with pressure, from 0.583 at 0 GPa to 0.652 at 20 GPa. If the isotropic Eliashberg electron-phonon coupling theory is used to simulate the effect on the critical temperature $T_c$, such an increase in $\lambda$ results in a substantial increase of $T_c$ from 2.5~K at 0 GPa to 4~K at 20 GPa. This shows that examining the effect of pressure offers a chance to resolve the pairing mechanism in ThCoC$_2$.

High-pressure study of the low- Z rich superconductor Be22Re

With $T_c \sim 9.6~\mathrm{K}$, Be$_{22}$Re exhibits one of the highest critical temperatures among Be-rich compounds. We have carried out a series of high-pressure electrical resistivity measurements on this compound to 30 GPa. The data show that the critical temperature $T_c$ is suppressed gradually at a rate of $dT_c/dP = -0.05~\mathrm{K/GPa}$. Using density functional theory (DFT) calculations of the electronic and phonon density of states (DOS) and the measured critical temperature, we estimate that the rapid increase in lattice stiffening in Be$_{22}$Re overwhelms a moderate increase in the electron-ion interaction with pressure, resulting in the decrease in $T_c$. High pressure x-ray diffraction measurements show that the ambient pressure crystal structure of Be$_{22}$Re persists to at least 154 GPa. We discuss the relationship between low-Z Be-rich superconductors and the high-$T_c$ superhydrides.

Mechanistic Study on Thermally Induced Lattice Stiffening of ZIF-8.

The flexibility of the ZIF-8 aperture, which inhibits a molecular cutoff of 3.4 Å, can be reduced by rapid heat treatment to obtain CO2-selective membranes. However, the early stages of the structural, morphological, and chemical changes responsible for the lattice rigidification remain elusive. Herein, using ex situ and in situ experiments, we determine that a small shrinkage of the unit-cell parameter, ∼0.2%, is mainly responsible for this transformation. Systematic gas permeation studies show that one needs to achieve this shrinkage without a disproportionately large shrinkage in the grain size of the polycrystalline film to avoid the formation of cracks. We show that this condition is uniquely achieved in a short time by exposure of ZIF-8 to a mildly humid environment where lattice parameter shrinkage is accelerated by the incorporation of linker vacancy defects, while the shrinkage in grain size is limited. The water-vapor-led incorporation of linker vacancy defects takes place with an energy barrier of 123 kJ mol–1, much higher than that for the thermal degradation of ZIF-8, <80 kJ mol–1. The latter is promoted by heat treatment in a dry environment at a relatively higher temperature; however, this condition does not shrink the lattice parameters at short exposure time.

Raman signatures of the distortion and stability of MgCO3 to 75 GPa

Abstract Knowledge of the stability of carbonate minerals at high pressure is essential to better understand the carbon cycle deep inside the Earth. The evolution of Raman modes of carbonates with increasing pressure can straightforwardly illustrate lattice softening and stiffening. Here, we report Raman modes of natural magnesite MgCO3 up to 75 GPa at room temperature using helium as a pressure-transmitting medium (PTM). Our Raman spectra of MgCO3 show the splitting of T and ν4 modes initiated at approximate 30 and 50 GPa, respectively, which may be associated with its lattice distortions. The MgCO3 structure was referred to as MgCO3-Ib at 30–50 GPa and as MgCO3-Ic at 50–75 GPa. Intriguingly, at 75.4 GPa some new vibrational signatures appeared around 250–350 and ~800 cm–1. The emergence of these Raman bands in MgCO3 under relatively hydrostatic conditions is consistent with the onset pressure of structural transition to MgCO3-II revealed by theoretical predictions and high-pressure and high-temperature experiments. This study suggests that hydrostatic conditions may significantly affect the structural evolution of MgCO3 with increasing pressure, which shall be considered for modeling the carbon cycle in the Earth's lower mantle.

Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder.

We investigated the effect of enhancement of superconducting transition temperature by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (LaSn, CaRhSn, YRhSn, LuRhSn; Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase in respect to the bulk one and proposed a model that explains the behavior in the series of nonmagnetic skutterudite-related compounds.

Carbon deficiency-induced changes of structure and magnetism of Mn3SnC

Crystal structure, magnetoelastic coupling, magnetization and magnetocaloric effects of Mn3SnC0.94 and Mn3SnC0.81 were investigated. Temperature-dependent high-resolution X-ray diffraction measurements showed that a larger carbon deficiency of Mn3SnC0.81 reduces lattice distortions more significantly than it reduces the lattice parameter. Resonant ultrasound spectroscopy measurements showed that the larger carbon deficiency has no effect on the lattice stiffening across a ferromagnetic transition, whereas it reduces the lattice softening across a low-temperature transition. Magnetic measurements showed that the larger carbon deficiency doubles high-field magnetization and improves the refrigeration capacity. It is suggested that the larger carbon deficiency of Mn3SnC0.81 weakens antiferromagnetic interactions more significantly than it enhances ferromagnetic interactions. However, the magnetocaloric effect of each sample includes a contribution from the lattice entropy change, which is not sensitive to the carbon deficiency.

Anomalous lattice stiffening in tungsten tetraboride solid solutions with manganese under compression

Tungsten tetraboride (WB4)-based solid solutions represent one of the most promising superhard metal candidates; however, their underlying hardening mechanisms have not yet been fully understood. Here, we explore the lattice compressibility of WB4 binary solid solutions with different manganese (Mn) concentrations using high-pressure x-ray diffraction (XRD) up to 52 GPa. Under initial compression, the lattices of low and high Mn-doped WB4 alloys (i.e. W0.96Mn0.04B4 and W0.84Mn0.16B4) are shown to be more and less compressible than pure WB4, respectively. Then, a c-axis softening is found to occur above 39 GPa in WB4, consistent with previous results. However, an anomalous sudden a-axis stiffening is revealed at ~36 GPa in W0.96Mn0.04B4, along with suppression of c-axis softening observed in WB4. Furthermore, upon Mn addition, a simultaneous stiffening of a- and c-axes is demonstrated in W0.84Mn0.16B4 at ~37 GPa. Speculation on the possible relationship between this anomalous stiffening and the combined effects of valence-electron concentration (VEC) and atomic size mismatch is also included to understand the origin of the nearly identical hardness enhancement in those two solid solutions compared to WB4. Our findings emphasize the importance of accurate bonding and structure manipulation via solute atoms to best optimize the hardness of WB4 solid solutions.

Restricting Lattice Flexibility in Polycrystalline Metal-Organic Framework Membranes for Carbon Capture.

Although polycrystalline metal-organic framework (MOF) membranes offer several advantages over other nanoporous membranes, thus far they have not yielded good CO2 separation performance, crucial for energy-efficient carbon capture. ZIF-8, one of the most popular MOFs, has a crystallographically determined pore aperture of 0.34 nm, ideal for CO2 /N2 and CO2 /CH4 separation; however, its flexible lattice restricts the corresponding separation selectivities to below 5. A novel postsynthetic rapid heat treatment (RHT), implemented in a few seconds at 360 °C, which drastically improves the carbon capture performance of the ZIF-8 membranes, is reported. Lattice stiffening is confirmed by the appearance of a temperature-activated transport, attributed to a stronger interaction of gas molecules with the pore aperture, with activation energy increasing with the molecular size (CH4 > CO2 > H2 ). Unprecedented CO2 /CH4 , CO2 /N2 , and H2 /CH4 selectivities exceeding 30, 30, and 175, respectively, and complete blockage of C3 H6 , are achieved. Spectroscopic and X-ray diffraction studies confirm that while the coordination environment and crystallinity are unaffected, lattice distortion and strain are incorporated in the ZIF-8 lattice, increasing the lattice stiffness. Overall, RHT treatment is a facile and versatile technique that can vastly improve the gas-separation performance of the MOF membranes.

Pressure-dependent phase transition of 2D layered silicon telluride (Si2Te3) and manganese intercalated silicon telluride

Two-dimensional (2D) layered silicon telluride (Si2Te3) nanocrystals were compressed to 12 GPa using diamond anvil cell techniques. Optical measurements show a color change from transparent red to opaque black indicating a semiconductor-to-metal phase transition. Raman scattering was used to observe the stiffening of the crystal lattice and subsequent phase behavior. A possible phase transition was observed at 9.5 ± 0.5 GPa evidenced by the disappearance of the A1g stretching mode. Si2Te3 was intercalated with elemental manganese to ∼ 1 at.%. Intercalation lowers the pressure of the proposed phase transition to 7.5 ± 1 GPa. Raman modes show both phonon stiffening and phonon softening, suggesting negative linear compressibility. These results provide fundamental insight into the high-pressure optical phonon behavior of silicon telluride and illuminate how a specific electron-donating intercalant can chemically alter pressure-dependent optical phonon behavior.

Compensated thermal conductivity of metallically conductive Ta-doped TiO2

Electrical and thermal conductivities of epitaxial, high-quality Ta-doped TiO2 (Ta:TiO2) thin films were experimentally investigated in the temperature range of 35–375 K. Structurally identified as the anatase phase, degenerate Ta doping leads to high electrical conductivity in TiO2, reaching &amp;gt;105 (Ω-m)−1 at 5 at. % of Ta, making it a potential candidate for indium-free transparent conducting oxides. In stark contrast, Ta doping suppresses the thermal conductivity of TiO2 via strong phonon-impurity scattering imposed by the Ta dopant which has a high mass contrast with Ti that it substitutes. For instance, the near-peak value shows a &amp;gt;50% reduction, from 9.0 down to 4.4 W/m-K, at just 2 at. % doping at 100 K. Interestingly, further Ta doping beyond 2 at. % no longer reduces the measured total thermal conductivity, which is attributed to a high electronic contribution to thermal conduction that compensates the alloy-scattering loss, as well as possibly the renormalization of phonon dispersion relation in the heavy doping regime originating from doping-induced lattice stiffening. As a result, at high Ta doping, TiO2 exhibits high electrical conductivity without much degradation of thermal conductivity. For example, near room temperature, 5 at. % Ta doped TiO2 shows over 3 orders of magnitude enhancement in electrical conductivity from undoped TiO2, but with only less than 10% reduction in thermal conductivity. The metallic Ta:TiO2 maintaining reasonable good thermal conductivity might find application in energy devices where good conduction to both charge and heat is needed.

The lattice stiffening transition in UO2 single crystals

The effective Debye temperatures () of the surface region of UO2 single crystals, prepared by the hydrothermal synthesis technique, were obtained from temperature-dependent x-ray photoemission in the temperature range of 300 K–623 K. A lattice stiffening transition, characterized by different regions of different effective Debye temperature, 500 ± 59 K below 475 K and 165 ± 21 K above 475 K is identified. A comparison of the temperature dependence of the effective UO2 Debye temperature, with the changes in the lattice expansion coefficient for UO2, support strong lattice-phonon interaction arising from the Jahn–Teller distortion.

Point defect engineering of high temperature piezoelectric BiScO3-PbTiO3 for enhanced voltage response

BiScO3-PbTiO3 is the most promising system among high sensitivity piezoelectric BiMO3-PbTiO3 perovskite solid solutions with high Curie temperature, which are under extensive investigation for expanding the operation temperature of state of the art Pb(Zr,Ti)O3 (PZT) up to 400°C. The viability of these alternative materials requires the development of specific point defect engineering that allow a range of piezoelectric ceramics comparable to commercial PZTs to be obtained, optimized for the different applications. A distinctive feature of BiMO3-PbTiO3 systems is the simultaneous presence of both Bi3+ and Pb2+ at the A-site of the perovskite. This enables the possibility of introducing charged point defects without incorporating new chemical species, just by defining an A-site non–stoichiometry. In this work, we present a comprehensive study of the effects of Bi substitution for Pb, along with the formulation of Pb vacancies for charge compensation. Results indicate an overall lattice stiffening that yields reduced polarizability and compliance, and dominates over a limited enhancement of the ferroelectric domain wall dynamics, so as a largely enhanced voltage response is obtained. Specifically, BiScO3-PbTiO3 with the A-site non-stoichiometry is shown to be very suitable as the piezoelectric component of magnetoelectric composites for magnetic field sensing.

High-pressure and temperature-induced structural, elastic, and thermodynamical properties of strontium chalcogenides

Pressure- and temperature-dependent mechanical, elastic, and thermodynamical properties of rock salt to CsCl structures in semiconducting SrX (X = O, S, Se, and Te) chalcogenides are presented based on model interatomic interaction potential with emphasis on charge transfer interactions, covalency effect, and zero point energy effects apart from long-range Coulomb, short-range overlap repulsion extended and van der Waals interactions. The developed potential with non-central forces validates the Cauchy discrepancy among elastic constants. The volume collapse (V P/V 0) in terms of compressions in SrX at higher pressure indicates the mechanical stiffening of lattice. The expansion of SrX lattice is inferred from steep increase in V T/V 0 and is attributed to thermal softening of SrX lattice. We also present the results for the temperature-dependent behaviors of hardness, heat capacity, and thermal expansion coefficient. From the Pugh’s ratio (ϕ = B T /G H), the Poisson’s ratio (ν) and the Cauchy’s pressure (C 12–C 44), we classify SrO as ductile but SrS, SrSe, and SrTe are brittle material. To our knowledge these are the first quantitative theoretical prediction of the pressure and temperature dependence of mechanical stiffening, thermally softening, and brittle nature of SrX (X = O, S, Se, and Te) and still await experimental confirmations.

Superconductivity in the presence of disorder in skutterudite-related La3Co4Sn13 and La3Ru4Sn13 compounds: Electrical transport and magnetic studies

La3Co4Sn13 and La3Ru4Sn13 were categorized as BCS superconductors. In a plot of the critical field Hc2 vs T, La3Ru4Sn13 displays a second superconducting phase at the higher critical temperature Tc⋆, characteristic of inhomogeneous superconductors, while La3Co4Sn13 shows bulk superconductivity below Tc. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds. Additionally, for La3Ru4Sn13 we find that dTc⋆/dP>dTc/dP. The pressure dependences of Tc are interpreted according to the McMillan theory and understood to be a consequence of lattice stiffening. The investigation of the superconducting state of La3CoxRu4−xSn13 shows a Tc⋆ that is larger then Tc for x < 4. This unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.

Effects of magnetic field intensity on carbon diffusion coefficient in pure iron in γ-Fe temperature region

Effects of magnetic field intensity on carbon diffusion coefficient in pure iron in the γ- Fe temperature region were investigated using carburizing technology. The carbon penetration profiles from the iron surface to interior were measured by field emission electron probe microanalyzer. The carbon diffusion coefficient in pure iron carburized with different magnetic field intensities was calculated according to the Fick's second law. It was found that the magnetic field intensity could obviously affect the carbon diffusion coefficient in pure iron in the γ- Fe temperature region, and the carbon diffusion coefficient decreased obviously with the enhancement of magnetic field intensity, when the magnetic field intensity was higher than 1 T, the carbon diffusion coefficient in field annealed specimen was less than half of that of the nonfield annealed specimen, further enhancing the magnetic field intensity, the carbon diffusion coefficient basically remains unchanged. The stiffening of lattice due to field-induced magnetic ordering was responsible for an increase in activation barrier for jumping carbon atoms. The greater the magnetic field intensity, the stronger the inhibiting effect of magnetic field on carbon diffusion.

Pressure effects on the superconductivity of theHfPd2AlHeusler compound: Experimental and theoretical study

Polycrystalline HfPd2Al has been synthesized using the arc-melting method and studied under ambient pressure conditions by x-ray diffraction from room temperature up to 450^oC. High pressure x-ray diffraction up to 23 GPa was also performed using Diacell-type membrane diamond anvil cells. The estimated linear thermal expansion coefficient was found to be {\alpha} = 1.40(3)x10^{-5} K^{-1}, and the bulk modulus derived from the fit to the 3rd order Birch-Murnaghan EOS (BMEOS) is B0 = 97(2) GPa. Resistivity studies under applied pressure (p < 7.49 GPa) showed a linear decrease of superconducting critical temperature with increasing pressure and the slope dTc/dp = -0.13(1) K GPa^{-1}. The same behavior is observed for the electron-phonon coupling constant {\lambda_{ep}}(p) that changes from 0.67 to 0.6, estimated for p = 0.05 GPa and 7.49 GPa, respectively. First principles electronic structure and phonon calculation results are presented and used to estimate the magnitude of electron-phonon interaction {\lambda_{ep}} and its evolution with pressure. Theoretical results explain the experimentally observed decrease in Tc due to considerable lattice stiffening.

Simultaneous characterization of protein coated iron oxide nanoparticles with nuclear inelastic scattering and atomic force microscopy

Bovine serum albumin coated magnetic iron oxide nanoparticles (IONPs), which were synthesized using a co-precipitation method with 57Fe have been subject to a combined study using atomic force microscopy (AFM) and nuclear inelastic scattering (NIS). The obtained partial density of vibrational states (pDOS) shows evidence for lattice stiffening and a pronounced mode at 23 meV compared to thin film magnetite at room temperature.

Elastic properties of the Zintl ferromagnet Yb14MnSb11

We report measurements of the elastic moduli as a function of temperature (5--300) K and magnetic field (0--2 T) for the Zintl ferromagnet Yb${}_{14}$MnSb${}_{11}$, which is believed to be a rare example of an underscreened Kondo lattice. The elastic moduli measured below the Curie temperature in this complex ferromagnet exhibit unusual lattice stiffening that is independent of the magnetic field and can be adequately modeled using the Landau theory.

Depression of the ferroelastic phase transition in LiCsSO4 by uniaxial stress

Abstract In the lithium-caesium sulphate crystal in the temperature range of ferroelastic phase transition, the uniaxial stress σ X induced changes in velocity and attenuation of the longitudinal ultrasonic wave propagating in the direction [010] are studied. The phase transition is close to the three-critical point and the critical exponent is κ = 0.27 ± 0.02. The stress applied drastically decreases the stepwise change in the wave velocity at T C up to its disappearance at 2 MPa. In the temperature range between T C and T C − 6 K, the stress leads to an increase in the wave velocity and a decrease in its attenuation. This range was interpreted as that of co-existence of ferroelastic and incommensurate ordering, in which the stress influences the density of solitons leading to stiffening of the crystal lattice.

Distinct effects of Al3+ substitution at Cu-site and Al2O3 addition on step-like elastic anomalies and electron–phonon coupling constant in EuBa2Cu3O7−δ superconductors

Abstract Ultrasonic longitudinal and shear velocities at 9 MHz were measured in temperature ranges of 80–280 K and 80–220 K, respectively, in EuBa 2 (Cu 1− x Al x ) 3 O 7− δ ( x = 0, 0.06 and 0.10) and EuBa 2 Cu 3 O 7− δ + y wt.% Al 2 O 3 ( y = 0.2 and 0.4) superconductors. A step-like elastic anomaly indicating sudden lattice stiffening was observed for x = 0 at around 260 K. Partial substitution of Al 3+ in place of Cu at x = 0.06 and 0.10 suppressed the step-like velocity anomaly and displayed monotonous velocity change with temperature. In contrast however, addition of Al 2 O 3 only shifted the anomaly to slightly lower temperatures. Interestingly, maximum T c was observed at x = 0.06 and this coincides with enhanced value of the computed BCS electron–phonon coupling constant, λ . The step-like elastic anomaly was discussed in terms of oxygen ordering involving Cu–O chains. Substitution of Al 3+ is suggested to go into Cu–O chain sites and effectively destroys oxygen ordering which in turn caused suppression of the elastic anomaly.